1. Field of the Invention
The present invention relates to actuators. More specifically, the present invention relates to control actuator systems for rolling missiles.
2. Description of Related Art
Future concepts for highly maneuverable tactical missiles require high performance airframes controlled by very high performance control actuator systems (CAS). Missile maneuvering is traditionally controlled using a cruciform arrangement of four aerodynamic control surfaces (e.g., control fins) with four actuator motors and gear trains that independently control the aerodynamic control surfaces. Conventional missile control actuator systems, however, can have very high power requirements, especially for missiles with a rolling airframe.
Rolling airframe missiles are designed to roll or rotate about their longitudinal axes at a desired rate (typically about 5 to 15 revolutions per second), usually to gain various advantages in the design of the missile control system. Small, rolling airframes, however, exacerbate CAS power density requirements, as the control fins must be driven to large amplitudes at the roll frequency of the missile to produce large maneuvers. In contrast with standard non-rolling missiles, rolling airframe missiles require constant movement of the control fins, thus expending energy throughout the flight. The required power increases linearly with roll rate and deflection angle. In order to achieve the high maneuverability desired in new missile designs, conventional control actuator systems would require power densities that are beyond those fielded in current missile systems.
Most prior approaches for reducing the power requirements of a control actuator system in a rolling missile have centered around minimizing hinge moments (due to aerodynamic loads), minimizing inertias at the control surface, and optimizing CAS design parameters. High gear ratio designs require very high CAS motor accelerations and speeds, leading to high current, high voltage motor designs. As the gear ratios are reduced, CAS motor speeds are reduced but CAS torque requirements increase as the control surfaces have more influence (inertia and hinge moments) on the CAS motor. Attempts to minimize hinge moments through hinge line placement are not always realized as the control surface center of pressure moves around with mach number. The typical solution has been to design the CAS to meet the power (torque/speed) requirements, even if excessive, and size the flight battery/power supplies accordingly.
Hence, a need exists in the art for an improved control actuator system for rolling missiles that requires less power than prior approaches.